If you are a self-employed person or a sole proprietor with no employees, you have access to one of the most powerful retirement tools of all: the solo 401(k) (also called individual 401(k) or one-participant 401(k)). It lets you contribute, with a strong tax advantage, much more than ordinary retirement plans allow, because you can contribute both as an employee and as your own employer. But how much can you actually contribute? The solo 401(k) calculator shows you the employee portion, the employer portion and the total contribution, taking the limits into account, so you know exactly how much you can set aside for retirement while saving on taxes.

What a solo 401(k) is

The solo 401(k) is a defined-contribution retirement plan reserved for self-employed people and sole proprietors with no full-time employees (with the exception, generally, of the spouse). It is the single-person version of the classic U.S. workplace 401(k) plan. Its distinctive feature is that, having no employees, you wear both hats: you are at the same time the "employee" who contributes a portion of their compensation and the "employer" who makes an additional contribution. This dual role allows you to reach much higher annual contributions than an ordinary individual plan. The contributions reduce the taxable income of the year (in the traditional version) and grow tax-deferred until withdrawal. It is a tool designed to let those who work for themselves set aside a lot, quickly.

How it works: you are employee and employer together

The mechanism that makes the solo 401(k) so powerful is the dual contribution. As your own employee you can contribute a portion of your income up to a fixed annual limit (the so-called elective deferral). As the employer you can make an additional contribution, calculated as a percentage of your net self-employment income (the profit sharing). The sum of the two portions is your total contribution, which cannot however exceed an annual overall limit. Since the employee portion is a fixed amount and the employer one is a percentage of income, those with medium-high incomes can approach or reach the overall limit. The calculator replicates exactly this logic: it computes the two portions separately, sums them and applies the overall limit, showing you how much you can contribute in total.

The employee portion (elective deferral)

The first component is the employee portion, or elective deferral: the part you contribute "as if" you were an employee directing part of their salary to their own 401(k). This portion has a fixed annual limit set by the rules (updated every year), the same for everyone regardless of income, and cannot in any case exceed your available income. The great advantage is that you can contribute up to this limit regardless of the percentage on income: even with a modest income you can set aside a substantial amount. If your income is below the limit, the employee portion is capped at the income itself. In the calculator you set the current deferral limit and the calculator uses the lesser of this limit and your net income: it is often the component that lets those with low or medium incomes still set aside a lot as a percentage.

The employer portion (profit sharing)

The second component is the employer portion, or profit sharing: the contribution you make as your own employer. It is calculated as a percentage of your net self-employment income — typically around 20% for a self-employed person (the exact percentage depends on the legal form and the calculation of net income, but the calculator lets you set it). On an income of 100,000, a 20% percentage gives 20,000 of employer portion. Unlike the employee portion (fixed), this one grows with income: the more you earn, the more you can contribute as employer, up to the overall limit. It is the lever that lets those with high incomes maximize contributions. The calculator computes this portion by multiplying the income by the percentage you set.

The annual overall limit

The sum of the employee portion and the employer one cannot exceed an annual overall limit, also set by the rules and updated year by year. This limit is the absolute cap on how much you can contribute to a solo 401(k) in a year (excluding any catch-up contributions for those over 50). If the sum of the two computed portions exceeds the limit, the total contribution is reduced to the limit: in practice the employer portion is "cut" just enough to fit. Those with a high income easily reach this cap and contribute the maximum allowed. In the calculator you set the current limit: if your portions exceed it, the calculation flags it and shows the contribution capped at the maximum. It is the way to understand whether you are fully using the tool or you still have room to contribute more.

Total contribution as income changes

Here is how the total contribution changes (with a 23,000 deferral limit, 20% employer percentage, 69,000 overall limit) as the net self-employment income varies:

The employee portion stays fixed, while the employer one grows with income until the total reaches the cap. From there on the contribution stops at the ceiling, regardless of how much more you earn.

Why it is so worthwhile: the tax advantage

The real reason the solo 401(k) is so valued is the tax advantage. In the traditional version, the contributions are deductible: they reduce the taxable income of the year in which you make them. If you set aside 43,000 and your rate is 30%, you save about 13,000 in taxes right away, besides setting aside for retirement. The investments inside the plan then grow tax-deferred: you do not pay taxes on interest, dividends and capital gains until you withdraw the money in retirement (when the rate is often lower). This double benefit — immediate deduction plus growth free of annual taxes — enormously accelerates the accumulation of capital compared to an investment taxed every year. Being able to contribute such high amounts (thanks to the dual contribution) multiplies the value of the tax advantage, and it is why the solo 401(k) is among the favorite tools of self-employed people with medium-high income.

Solo 401(k) versus other plans for the self-employed

The solo 401(k) is not the only retirement tool for those who work for themselves, but it is often the most generous. Compared to a SEP-type plan, which allows only the "employer" contribution (a percentage of income), the solo 401(k) adds the employee portion at a fixed amount: this allows, especially at medium incomes, contributing much more for the same income, because you sum the fixed portion to the percentage. At very high incomes, where both reach the overall limit, the difference narrows. Compared to ordinary individual savings plans, the solo 401(k) has much higher contribution limits. In exchange it requires a bit more administrative management. The calculator helps you see the potential of the solo 401(k) in your situation; to choose between different tools it is worth comparing the possible contributions and the complexity of each with an advisor.

Employer portion as the percentage changes

Here is how the employer portion (and therefore the total contribution) changes on an income of 100,000, with a 23,000 deferral limit, as the employer contribution percentage varies:

The employer percentage is an important lever: the higher it is, the more you contribute, up to the cap. The effective applicable percentage depends on the legal form and the calculation of net income, so check it with an advisor.

Catch-up contributions

Those who have passed a certain age (generally 50) can contribute, beyond the ordinary limits, a catch-up contribution: an additional portion on the employee part, designed for those approaching retirement who want to accelerate the accumulation. This extra contribution adds to the ordinary deferral limit and also raises the reachable overall limit. In practice, a self-employed person over 50 can contribute a few thousand more per year than a younger one with the same income. The calculator works with the limits you set: if you fall into the age bracket that gives the right to the catch-up, enter a deferral limit and an overall limit already inclusive of the catch-up portion to estimate your effective maximum contribution. It is a valuable possibility in the last years of a career, when income is often higher and there is more savings capacity.

Roth solo 401(k) versus traditional

The solo 401(k) can be traditional or Roth, and the choice changes when you pay the taxes. In the traditional, the contributions are deductible today and you pay taxes at withdrawal: it is worth it if you expect a lower rate in retirement than today. In the Roth, you contribute with already-taxed money (no deduction today) but the withdrawals in retirement are tax-free, including the capital gains: it is worth it if you expect a higher rate in the future or want certainty on future taxes. The employee portion can generally be Roth; the employer one is typically traditional (although the rules evolve). The calculator estimates the amount of the contribution, which is the same in the two versions; the choice between Roth and traditional concerns the tax treatment, not the amount. Assess this choice based on your expectations about future rates, ideally with an advisor.

Who can open a solo 401(k)

The solo 401(k) is reserved for those who have self-employment income and no full-time employees other than the spouse. It can be opened by freelancers, sole proprietors, consultants, independent contractors, individual entrepreneurs and, in some cases, small partnerships or corporations with only the owner (and possibly the spouse) working in them. The presence of a non-spouse employee who works beyond a certain hours threshold generally makes eligibility lapse, because the plan should then cover them too. It is therefore the ideal tool for those who really work alone. The eligibility rules are specific and vary by jurisdiction and legal form; the calculator assumes you are eligible and estimates the possible contribution. Before opening it, verify that you meet the requirements with a professional.

Solo 401(k) and other tools compared

Here is a comparison between the solo 401(k) and other retirement tools for the self-employed:

The solo 401(k) almost always wins on the maximum contribution thanks to the dual portion; the others can be simpler to manage. The choice depends on income, desire to maximize and tolerance for administrative management.

Mistakes and cautions

Some caution in using the solo 401(k). First: do not contribute more than the cap — an excess of contributions carries penalties; the calculator helps you precisely stay within the limits. Second: remember that the effective employer percentage depends on the calculation of net income (after certain deductions), so the "real" percentage may differ from the nominal one: check with an advisor. Third: do not set aside more than your current liquidity allows — the funds in a 401(k) are locked until retirement, with penalties for early withdrawals. Fourth: if you hire a non-spouse employee, you might lose eligibility. The calculator gives you an estimate of the possible contribution, but does not replace the verification of the requirements, the exact income calculation and the updated limits, which must always be confirmed with a professional.

How the calculator works

Enter your net self-employment income, the current employee portion limit (deferral), the employer contribution percentage and the annual overall limit. The calculator returns the total contribution to the solo 401(k), the employee portion, the employer portion and the percentage of income you are setting aside, with an assessment. Try different income levels and employer percentages to see how much you could contribute and whether you reach the cap. It is the quickest way to understand the potential of the solo 401(k) in your situation and plan how much to direct to retirement with a tax advantage.

The data you need

You need four data. The net income from self-employment, the base on which the contributions are computed. The employee portion limit (deferral) provided for the current year in your system. The employer contribution percentage applicable to your situation (often around 20% for a self-employed person). The current annual overall limit. The result is the total contribution you can make, split between employee portion and employer portion, with the percentage of income set aside. Remember that the exact limits, the real percentage and the requirements vary by year and jurisdiction: use the estimate to plan, but always confirm the precise amounts with a tax or retirement advisor.

A worked example

Imagine a self-employed person with a net income of 100,000, a deferral limit of 23,000, an employer percentage of 20% and an overall limit of 69,000. The employee portion is the lesser of 23,000 and the income, that is 23,000. The employer portion is 100,000 × 20% = 20,000. The total contribution is 23,000 + 20,000 = 43,000, equal to 43% of income, well below the cap. Try raising the income to 300,000: the employer portion would rise to 60,000, but the total (83,000) would exceed the cap, so it is capped at 69,000. It is the way to understand how much you can contribute and when you reach the ceiling.

Frequently asked questions

What is a solo 401(k)?

It is a defined-contribution retirement plan for self-employed people and sole proprietors with no employees (other than the spouse). It is the single-person version of the workplace 401(k): you can contribute both as an employee and as your own employer, reaching much higher contributions than an ordinary individual plan, with a tax advantage.

Why can I contribute so much?

Because you contribute twice: as an employee (a fixed portion up to an annual limit, the elective deferral) and as an employer (a percentage of net income, the profit sharing). The sum, within an overall cap, is much higher than an individual plan with only one type of contribution allows.

How is the maximum contribution calculated?

Employee portion = lesser of the deferral limit and income; employer portion = income × percentage; total = sum of the two, capped at the annual limit. Example: income 100,000, deferral 23,000, employer 20% → 23,000 + 20,000 = 43,000. On high incomes you reach the cap (e.g. 69,000).

What is the difference between employee and employer portion?

The employee portion (deferral) is a fixed amount up to an annual limit, the same for everyone regardless of income (but not above the income itself). The employer portion is a percentage of net income, so it grows with income. The first helps low/medium incomes, the second helps high incomes maximize.

What happens if I exceed the cap?

The total contribution is capped at the annual overall limit: in practice the employer portion is reduced just enough to fit. The calculator flags it. Contributing more than the cap carries tax penalties, so it is important to respect the ceiling.

What tax advantage does it have?

In the traditional version the contributions are deductible (they reduce the taxable income of the year) and the investments grow tax-deferred until withdrawal. Double benefit: immediate saving plus growth free of annual taxes. Being able to contribute high amounts multiplies the value of the advantage.

Solo 401(k) or SEP: which is better?

The SEP allows only the employer contribution (a percentage of income). The solo 401(k) adds the fixed employee portion, so at medium incomes it lets you contribute much more. At very high incomes, where both reach the cap, the difference narrows. The solo 401(k) also offers the Roth option.

What are catch-up contributions?

They are an additional portion that those who have passed a certain age (generally 50) can contribute beyond the ordinary limits, on the employee part. They raise both the deferral limit and the overall cap. In the calculator, if you are entitled, enter limits already inclusive of the catch-up.

What is the difference between Roth and traditional?

In the traditional you deduct today and pay taxes at withdrawal; in the Roth you contribute with already-taxed money but the withdrawals are tax-free. The traditional is worth it if you expect a lower rate in retirement, the Roth if higher. The contribution amount is the same; only the tax treatment changes.

Who can open a solo 401(k)?

Those who have self-employment income and no full-time employees other than the spouse: freelancers, sole proprietors, consultants, independent contractors. Hiring a non-spouse employee beyond a certain threshold generally makes eligibility lapse. Check the specific requirements of your jurisdiction with a professional.

Is the employer percentage always 20%?

No, it is a typical value but the effective percentage depends on the legal form and the calculation of net income (after certain deductions). For a self-employed person it is often around 20% of net income; for other forms it may differ. Check the real applicable percentage with an advisor.

What data do I need?

Four: the net self-employment income, the year employee portion limit (deferral), the employer contribution percentage and the annual overall limit. The result is the total contribution, split between employee and employer portion, with the percentage of income set aside.

Does the calculator replace an advisor?

No, it is an informational tool to plan. The exact limits (updated every year), the real employer percentage, the eligibility requirements and the tax treatment vary by year and jurisdiction. Use the estimate to understand the potential, but always confirm the precise amounts with a tax or retirement advisor.

Updated July 2026